In his first-ever interview, the sole Australian survivor of the Waco siege has revealed to 60 Minutes what really took place during the 51-day stand-off, and why he believes crazed cult leader David Koresh will one day return to Earth as the son of God.

NSW police know who killed security guard

Detectives investigating the fatal shooting of a security guard four years ago believe they know who did it, and have forensically linked the case to two other violent Sydney crimes.

Gary Allibon, 59, was shot during the armed robbery of a cash delivery van in Sydney's CBD early on June 7, 2010.

In a statement on Friday, Detective Superintendent Luke Moore said a chain of events linked to Mr Allibon's death had been pieced together and police were confident they knew who was responsible for the killing.

"Let me be clear: Gary Allibon was by all accounts a law-abiding, fair-minded and very decent man who was in the wrong place at the wrong time," Supt Moore said.

"He died because one of the men involved in the robbery decided to shoot him in the back and steal his gun."

Police believe three cars were used by those involved Mr Allibon's shooting: a white BMW X5; a stolen high-performance Audi S8 sedan, which was involved in the shooting of another man in Wentworthville in April, 2009; and a silver 2004 BMW 5-Series sedan, stolen during a violent car-jacking in Maroubra in July 2009.

Supt Moore said on the day Mr Allibon was killed the occupants of the white BMW X5 parked in Ascot Street, Kensington and got into the silver BMW 5-Series sedan and drove to Harbourne Lane where they met up with the Audi.

The Audi took four men to the CBD, was involved in a minor crash about 6am (AEST), and arrived at Sussex Street 10 minutes later.

Three of the men then robbed the cash delivery van, with one shooting Mr Allibon, he said.

"While I can't go into specifics, I can confidently say that we believe those who were responsible for shooting a man multiple times in Wentworthville in April 2009, were also involved in the robbery and shooting which resulted in Mr Allibon's death.

"We believe we know who killed Mr Allibon, but we need some more assistance from the public to help us get across the line and make an arrest."